2. FMO3 is an enzyme that helps break down a chemical in humans, trimethylaamine

Question

2. FMO3 is an enzyme that helps break down a chemical in humans, trimethylaamine, that produces the smell of rotting fish. The gene for FMO3 is located on chromosome 1. The functioning form of the enzyme is coded for by a dominant allele, and the nonfunctioning form of the enzyme is coded for by a recessive allele. Individuals with the nonfunctioning from of the enzyme have trimethylaminuria, also known as fish odor syndrome. Neither Maggie nor Mark has the fish odor syndrome, but their daughter Melissa does. If Maggie and Mark have another baby, what is the chance that child will also have fish odor syndrome?

Explanation / Answer

This syndrome is a recessive disorder, and hence needs two alleles to manifest the syndrome.

Here, both the parents do not have the syndrome, but their daughter does. It means, both the parents are carriers, and are heterozygous. In such case, heterozygous parents have 25% of chance of having children with the syndrome, and 75% chances of having non-affected children.

So, they have 0% chance of having a child with the fish odor syndrome.

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